1. Field of the Invention
This invention relates to the prevention and treatment of Streptococcus suis infections by means of an antiserum obtained by hyperimmunization of horses.
2. Information Disclosure Statement
DeMoor, Antonie van Leeuwenhoek, 29:272-280 (1963) reported the discovery of three new serological groups of Streptococci which were responsible for septicemic infections in pigs. These three groups, denoted Lancefield R, S and T, exhibited beta-hemolysis on horse blood agar and acid production from inulin. The serologically distinctive antigens were cell wall polysaccharides.
Elliot, J. Hyg. Camb., 64: 205-212 (1966) studied the causative agent of certain outbreaks of streptococcal infection. This agent, "PM streptococcus," was serologically identical to Field's strain 428 and De Moor's group S streptococcus, but Elliot assigned them to Lancefield Group D. However, in view of the differences between PM streptococcus and other group D organisms, Elliot proposed designating a new subgroup, Streptococcus suis, and assigning the PM strains to "Capsular Type 1." De Moor's group R were later designated "Capsular Type 2." See Windsor and Elliot, J. Hyg. Camb., 75: 69-78 (1975). Other types have since been identified. See Perch, et al., J. Clin. Microbiol, 17(6): 993-996 (1983). Streptococcus suis infections in pigs and humans have been reported in Europe and other countries as early as 1954. An increased awareness of the problem by practitioners and diagnosticians in the United States has recently resulted in a dramatic rise in case reports of S. suis problems in pigs of all ages. The disease may vary from subclinical infection to death. Some conditions and disease attributed to S. suis infections in swine are as follows:
______________________________________ Meningitis "Fading pig syndrome" Arthritis Fibrinopurulent pericarditis Pneumonia Haemorrhagia necrotizing myocarditis Septicemia Vegetative valvular endocarditis Vaginitis Abortion ______________________________________
Clinical signs of the infection include various combinations of anorexia, depression, reddening of the skin, fever, incoordination, swollen joints, blindness, deafness, and lameness. In peracute cases of septicemia or meningitis, there may be no premonitory clinical signs and pigs may just be found dead.
Streptococcus suis is commonly found in the upper respiratory tract and tonsils of pigs in most areas of the world in which swine are raised. Within an infected herd, virtually all pigs carry the organisms in their tonsillar crypts, and farrowing sows probably transmit the organism to young pigs through nasal contact. The bacterium may survive in feces for a week and in decomposing carcasses for almost 2 weeks. Fortunately, the organism is highly susceptible to most cleaning and disinfecting agents. Hadley and Enright, Vet. Res. 114:585-87 (1984).
Eradication through depopulation has been suggested, but most veterinarians recommend control by improving management practices and administering antibiotics when necessary. The organism is susceptible to penicillin in vitro, and antibiotic treatment is usually effective in acute cases, but is not necessarily favorable in chronic cases. Control by in-feed medication is only economic on the more severely affected farms. S. suis can persist in the tonsils in the presence of therapeutic levels of antibiotics and can persist in the environment for prolonged periods. Good management techniques may minimize the risks of S. suis infections in swine herds. It has been suggested to avoid overcrowding, poor ventilation, and other stressful conditions in the pig houses, especially when young pigs are mixed and moved to the nursery. All-in/all-out rearing as well as cleaning and disinfecting the premises between groups may help in control of outbreaks Erickson, JAVMA 191(11):1391-93 (1987).
Azuma, et al., Nat. Inst. Anim. Health Q. (Jpn.) 23:117-126 (1983) prepared antisera against Strep. suis by culturing the organism in a Todd-Hewitt broth, inactivating with pepsin, and inoculation the bacterin intravenously into rabbits on a daily basis for 12 successive days. The antisera were used only for serological typing. Perch likewise prepared anti-Strep. suis antisera by immunization of rabbits; again, there was no teaching of therapeutic or prophylactic utility.
Elliot reported that serum of piglets convalescent from Str. suis type 1 infections could protect susceptible animals from infection with "homologous streptococci." Piglets and horses, of course, are "heterologous."
The hyperimmunization of a horse with Escherichia coli or Salmonella, both gram negative rod-type bacteria, in order to obtain immune serum for use in man is known. Le Minor, U.S. Pat. No. 3,992,521. However, this technique has not been used in the preparation of Streptococcus suis (gram positive cocci-type bacteria) antiserum, and the use of such antiserum in immunization has not been reported.